Fusion of lumbar vertebrae is performed under circumstances including those in which degenerative disk disease, scoliosis, or other deformity indicates that stopping motion between adjacent vertebral segments is desirable. The fusion procedure entails inserting a bone graft between vertebral elements thereby inducing bone growth that ultimately fuses the adjoining vertebral elements. In order to accomplish the fusion of lumbar vertebrae in a minimally invasive manner, procedures, such as those performed in accordance with the Pathfinder™ System of Abbott Spine of Austin, Tex., provide for insertion and retention of a stabilizing rod between pedicle screws, one of which is anchored into each of the adjoining vertebrae, so as to maintain them at a fixed relative displacement after the graft has been inserted and until the biological response completes the fusion process.
It should be noted that lumbar fusion surgery may require relative positioning of adjacent vertebrae in various planes, whether by relative distraction or compression of the inter-vertebral space, or by reduction, i.e., displacement of a vertebra in a plane transverse to the axis of the spine, i.e., in a direction that will be referred to herein as ‘vertical,’ as referred to a prone patient.
Using minimally invasive surgical procedures, lumbar fusion surgery is begun as now described with reference to FIG. 1. A first incision 10 is performed in the patient's back 12, parallel to the spine 14 and to one side. Though this incision, pedicle screws 16 and 18 are inserted, by known procedures, into the pedicles of adjoining vertebrae 20 and 22, such as lumbar vertebrae L4 and L5. Rod 24 is inserted through slotted guides in each of pedicle screws 16 and 18 and secured with respect to each of the pedicle screws by closure tops that are threaded for retention in a corresponding helical thread of the pedicle screws. The rest of the procedure proceeds via a second incision 26 made parallel to the first incision 10 and laterally opposite to the first incision on the other side of the spine. Edges of the second incision are held apart by a retractor 28 so that a graft 30 may be inserted between vertebrae 20 and 22. Retractor 28 is typically tethered, via flexible arm 32, to a mounting 34 fixed with respect to the operating table. This method of mounting retractor 28 is unwieldy and not as convenient for the surgeon's unfettered access to the surgical site as might be desired.
It is desirable for reasons both of convenience and sterility that a method and apparatus be provided whereby forces may be applied to a bone, such as a vertebra, with respect to a local fulcrum, and also that a method and apparatus be provided for supporting a retractor 28 locally to the region of the surgery.